Date: 2011jun25 OS: Windows Q. How does windows check if I have a good internet connection? A. Its NCSI (Network Connectivity Status Indicator) checks that:

dns.msftncsi.com resolves to 131.107.255.255 using DNS http://www.msftncsi.com/ncsi.txt contains exactly: Microsoft NCSI with no newlines or other non-printing characters.

More info http://technet.microsoft.com/en-us/library/cc766017%28WS.10%29.aspx Apple devices use

http://captive.apple.com Which returns "Success" in some HTML.

Another old faithful is

http://example.com